Name __________________________________
NUTR 543 – Advanced Nutritional Biochemistry
Exam 1 – Summer 2007
Multiple Choice
1) Which of the following characteristics best describes an allosteric enzyme?
a) The substrate saturation curve obeys Michaelis-Menten kinetics.
b) The affinity for substrate is increased by an allosteric inhibitor.
c) The substrate saturation curve is shifted to the right by an allosteric
inhibitor.
d) The allosteric site is on a separate subunit from the catalytic site.
e) The response to increasing substrate concentration is desensitized by
positive cooperativity.
2) Which of the following is generally NOT a characteristic of regulatory
enzymes?
a) Catalyzes an irreversible reaction
b) Catalyzes a rate limiting reaction
c) Exhibits hyperbolic kinetics (Michaelis-Menten kinetics)
d) Catalyzes a reaction early and unique to a metabolic pathway.
e) All of the above are characteristic of regulatory enzymes.
3) Allosteric activation of PFK-1 by AMP is an example of:
a) Regulation of enzyme activity by Non-covalent interaction
b) Covalent regulation of enzyme activity
c) Changes in enzyme abundance
4) The Km of lipoprotein lipase (LPL) is 10 times higher in adipose tissue than in
cardiac tissue. Consequently, the binding affinity of LPL is ______ in adipose
tissue than cardiac tissue.
a) Higher
b) Lower
c) Cannot tell as Km is related to the ability of the enzyme to convert the
substrate to the product.
5) Glucose-6-phosphate is an example of a V-type of allosteric inhibitor of
hexokinase. Consequently, G6P will _______ of hexokinase.
a) Increase the Vmax
b) Decrease the Vmax
c) Increase the Km
d) Decrease the Km
6) Exercise can increased the activity of phosphorylase kinase and therefore the
catabolism/mobilization of glycogen by
a) Increases synthesis of phosphorylase kinase by glucagons
b) Non-covalent binding by calcium-bound calmodulin protein
c) Allosteric activation by ATP
d) Covalent activation by insulin
e) None of the above increases the activity of phosphorylase kinase
7) Insulin’s effect on the activity of intracellular tyrosine kinase is thought to
occur by
a) Intracellular receptors that increases the transcription of the gene for
tyrosine kinase.
b) Ligand-gated receptors
c) Catalytic receptors
d) G-protein linked receptors
8) Jane, a 27-year-old woman who is an insulin-dependent diabetic, went on a
weekend cross-country ski trip and forgot to pack her insulin. Analysis of a
blood sample taken when Jane returned home most likely revealed:
a) Unchanged levels of hemoglobin A1c
b) No detectable ketones
c) Below normal levels of blood glucose
d) Below normal levels of glucagon
e) Below normal levels of fatty acids
9) Which of the following metabolic alterations are likely to have occurred to
Jane over the weekend?
a) Decreased gluconeogenesis
b) Increased oxidation of fatty acids by the liver
c) Decreased breakdown of skeletal muscle protein
d) Increased oxidation of fatty acid by RBC’s
10) Which of the following changes in blood chemistry would have been seen in
Jane after the weekend?
a) Hypoglycemia
b) Elevated free fatty acids
c) Ketosis
d) Two of the above
e) All of the above
11) Which of the following is NOT true regarding insulin’s effect on tissues.
a) Increases glycolysis in the liver
b) Decreases glycolysis in the adipose
c) Increases glycogen synthesis in muscle
d) Increases activity of lipoprotein lipase in adipose and subsequent uptake
of fatty acids
e) Increases pyruvate dehydrogenase activity in the liver
12) Which of the following is NOT true regarding glucagon’s effect on tissues.
a) Increases triglyceride degradation in adipose
b) Increases gluconeogenesis in the liver
c) Increases fatty acid oxidation in the liver
d) Decreases protein degradation in the muscle
e) All of the above are true
13) Long-term complications associated with poor glycemic control in diabetics is
thought to be caused by:
a) Elevated hemoglobin A1c
b) Accumulation of sorbitol and glycosylated proteins
c) Activation of hormone-sensitive lipase (HSL)
d) Hemolysis due to deficiency in glucose-6-phosphate dehydrogenase
e) All of the above contribute directly to long-term complications of diabetes
14) The protein toxin produced by V. Cholera is thought to:
a) Cause a reduction in the ratio of NADH:NAD
b) Reduced production of lactate in muscle
c) Bind to Gs proteins and permanently activate them
d) Inhibit transport of chloride out of the intestinal cell into the lumen
e) Decrease cAMP levels in the intestinal cell resulting in the inhibition of
cAMP-dependent phosphoryation of membrane proteins involved in ion
transport.
15) A total deficiency of which of the following enzymes would most directly
compromise the ability of RBC’s to pump sodium out of the cell?
a) Enolase
b) Pyruvate carboxylase
c) 3-phosphoglycerate kinase
d) phosphoglycerate mutase
e) lactate dehydrogenase
16) Which of the following pairs of enzymes in glycolysis is allosterically regulated
in skeletal muscle?
a) Glucokinase and PFK-1
b) Hexokinase and aldolase
c) PFK-1 and 3-posphoglycerate kinase
d) Pyruvate kinase and lactate dehydrogenase
e) Hexokinase and pyruvate kinase
17) Which of the following is NOT a function of glycolysis?
a) Only source of energy in red blood cells
b) Directly produces NADPH for energy production
c) Produces intermediates that can be converted to alpha-glycerol phosphate
for triglyceride synthesis
d) Oxidizes glucose to pyruvic acid in the liver for possible synthesis of fatty
acids
e) Can produce energy with inadequate oxygen levels during severe
exercise.
18) At rest, the muscle’s utilization of glucose as a source of energy is
a) Inhibited by elevated ATP levels
b) Activated by elevated cAMP levels
c) Inhibited by elevated citrate levels
d) A and C
e) All of the above
19) During starvation, glucose utilization in the liver is regulated by:
a) Increased synthesis of glucokinase
b) Decreased concentration of glucagons
c) Concentration of liver glucose below the Km of glucokinase
d) Decreased activity of GLUT-4
e) None of the above
20) During moderate intensity exercise (jogging), glucose utilization by muscle is
regulated by:
a) Decreased activity of PFK-2
b) Decreased concentration of glucose-6-P
c) Inhibition of GLUT-2 by insulin
d) Inhibition hexokinase by elevated levels of ATP and citrate
e) Activation of glucokinase by feed-forward activation by high glucose
21) A deficiency in which of the following enzymes in the RBC is most likely to
result in hemolytic anemia?
a) Glucose-6-phosphatase
b) NADPH oxidase
c) Myeloperoxidase
d) Transketolase
e) Glucose-6-phosphate dehydrogenase
22) Glucose-6-phosphate dehydrogenase is
a) Inhibited by NADPH
b) Inhibited by NADH
c) Inhibited by ATP
d) Activated by fructose-2,6-bisphosphate
e) Activated by AMP
23) Which of the following is not a phase of the Pentose Phosphate Pathway
a) ATP synthesis
b) Oxidative phase producing NADPH
c) Non-oxidative phase producing a variety of monosaccharides of different
sizes
d) All of the above are part of the PP Pathway
e) None of the above are part of the PP Pathway
24) Superoxide anion is produced in red blood cells
a) When the iron in hemoglobin is reduced to ferrous iron (Fe++)
b) When glutathione peroxidase converts oxygen to superoxide
c) Only in the absence of the Pentose Phosphate Pathway
d) During the spontaneous oxidation of hemoglobin bound oxygen
e) In Superman when exposed to kryptonite.
25) NADPH is NOT used for
a) Synthesis of many steroid hormones
b) Synthesis of fats
c) Synthesis of glucose (gluconeogenesis)
d) De-toxification reactions in the liver using the Cytochrome P-450 system
e) Reduction of oxidized glutathione by glutathione reductase
26) Describe how the utilization of glucose (glucose uptake and phosphorylation
of glucose) by the liver is regulated in the post-absorptive state. Also
describe the rationale behind this mechanism of regulation.
In the post-absorptive state, the liver should not be
using glucose and allow other tissues that require this
fuel to use it. To achieve this, the Km of glucokinase is
well above the concentration of glucose in the cell in the
post-absorptive state. Thus, glucose will not be
phosphorylated by glucokinase and diffuse back into
the blood.
27) Describe why the regulation of glycolysis in the muscle is different than its
regulation in the liver.
Glycolysis functions in the muscle primarily as a source
of energy, particularly during exercise. In contrast,
glycolysis in the liver functions to convert excess
dietary carbohydrates to fats during feeding.
Consequently, glycolysis in the muscle is regulated be
the energy status of the cell while in the liver, it is
regulated by the amount of glucose and the presence of
insulin/glucagon (reflecting the fed/fasted states)
28) Describe how PFK-1 in the liver is regulated during active feeding. Also
describe the rationale behind this mechanism of regulation.
During active feeding, levels of PFK-1 are high due to
induction by insulin. In addition, the elevated levels of
F6P allosterically activates PFK-2, producing F1,6DP
which in turns allosterically activates PFK-1 (and
overrides PFK-1’s inhibition by ATP & citrate). Lastly,
PFK-2 is covalently activated by dephosphorylation by
PFK-2 phosphatase, an enzyme induced by insulin.
Rationale: during active feeding, increased hepatic
glycolysis allows the liver to convert excess
carbohydrates to triglycerides for storage.
29) Describe, in the space given, how a genetic deficiency in glucose-6phosphate dehydrogenase results in excessive hemolysis following the
consumption of fava beans.
A genetic deficiency of G6PD results in a reduced ability
to produced NADPH in the Pentose phosphate pathway.
With inadequate NADPH production, reduced
glutathione will be in short supply and glutathione
peroxidase will not be able to remove the hydrogen
peroxide produced from the superoxide generated
spontaneously from the oxidation of hemoglobin
carrying oxygen. Chemicals found in fava beans have
been known to increase oxidative stress in RBC’s in
individuals with G6PDH deficiency.